1. Field of the Invention
The present invention relates to a platform assembly with a movable platform operable in an oscillatory motion so that a subject on the platform moves in a headwards and footwards direction with the platform. Currently contemplated applications of the invention will utilize variations in the speed, frequency and symmetry of oscillatory movement of the platform and include at least the following: sleep induction, apnea prevention, awakening functions, relief from restless legs syndrome and painful legs and moving toes syndrome, non-invasive motion ventilation, non-invasive vibratory ventilation, non-invasive cardiopulmonary resuscitation, non-invasive counter pulsation, augmentation of stroke volume, non-invasive cardiopulmonary bypass support, mediator release, and stimulation of bowel motility.
2. Description of the Related Art
It has long been recognized that many physiological characteristics such as breathing rates and heartbeats of humans and other animals are cyclic and that bodies respond to certain types of oscillatory stimulations with beneficial results. For instance, parents have long recognized that rocking a baby back and forth in a headwards-footwards direction soothes their child and hastens the onset of the infant's sleep. Many devices have been designed and marketed to accomplish this end. In addition to parental observation, scientific evidence indicates that babies have better developed proprioceptive-vestibular receptive systems than adults. This scientific evidence has been the basis for the development of devices which seek to soothe the baby in a simulated maternal development environment through such features as movements in a specially designed bed to simulate the mother's walking while the baby was a fetus, in conjunction with simulated sounding of maternal breath sounds, heart sounds and gastrointestinal sounds within such a system.
Furthermore, it appears that gentle, small oscillations on a waterbed may diminish the frequency of apneas in preterm infants. Prior art devices for preventing apnea include air mattresses with a bubble chamber, devices which induce auditory stimulation, devices which induce a vibration in a peripheral sensory area of the infant, a bed with a suspension and drive system to simulate motion experienced by a fetus while the mother is walking, and apparatus for producing mechanical vibrations which simulate the mother's heartbeat. These devices are passive in that they constantly produce their aural or mechanical stimulants. Others use non-invasive respiratory monitoring systems to trigger external stimulants to end an adverse cardiorespiratory event, such as an apneic event. Such triggered systems employ harsher rocking motions and vibrations to terminate the adverse cardiorespiratory events. For example, it is recommended that the baby be stimulated by touching and gently shaking to cause awakening and thereby terminate an apneic event.
As mentioned above, the breathing rate of a respiratory system is a cyclical physiological function of the body. Many forms of vibration and oscillatory stimuli which utilize the cyclical characteristics of the respiratory system are used for medical and/or experimental purposes. For instance, it is known that external chest vibrations in combination with tracheal gas insufflation, which is a form of high frequency vibration ventilation (HFVV), is an effective means of artificial ventilation in experimental animals. For example, when anesthetized paralyzed dogs are placed in the lateral decubitus position with their chest on a vibrating plate at a frequency of 15-30 Hz and an amplitude of 2-4 mm upward and downward, and a low flow of air is insufflated into the trachea at the level of the carina, adequate gas exchange is maintained. It has also been found that vibration of the chest wall reduces breathlessness. Vibration of the chest wall inspiratory muscles during inspiration (in-phase) reduces breathlessness associated with hypercapnia and resistive loading in normal subjects and patients with chronic obstructive lung disease. Vibration is typically applied using two standard physiotherapy vibrators--at a vibration amplitude of 2 mm at 120 Hz--manually triggered from the inspiratory flow signal displayed on a storage oscilloscope. However, no devices or methods are known where vibration or any other oscillatory motion alone will support ventilation.
Conventional positive pressure mechanical ventilators or positive pressure high frequency oscillatory ventilators support ventilation by repeatedly introducing volumes of air into the lungs and then releasing. A problem with these conventional methods of supporting ventilation is that a rather large pressure is required to inflate the lungs. The high positive pressure inflations of the lungs created by mechanical ventilators may damage the lungs in a phenomenon designated "barotrauma". Recent studies have made it apparent that lung injuries may also result from high tidal volumes or "volutrauma", the main determinant of which is the end-inspiratory volume. A ventilator that adequately exchanges gasses in the lungs and that requires less pressure in the lungs would reduce the effects and/or the occurrences of "barotrauma" and "volutrauma". High frequency oscillation ventilation is used with reduced acute and chronic lung injury. However, conventional high-frequency oscillation ventilation requires the insertion of an intubated airway which may not be appropriate under some of the circumstances in which mechanical ventilatory support is required.
The heart beat is another cyclical physiological function of the body. Many medical procedures, such as cardiovascular resuscitation, take advantage of the cyclical nature of the heart rhythm. Although many manual and automatic methods have been utilized for cardiopulmonary resuscitation, the perfect method has yet to be described. Active mechanical compression and decompression is the most recent method to be advocated; its advantage over standard compression is that the addition of active decompression facilitates venous return as intrathoracic pressure becomes negative relative to atmospheric pressure. And recently, a CPR method using a phased chest and abdominal compression-depression with a Lifestick.RTM. resuscitator for CPR was reported; this method suggests that active compression and decompression of both the thorax and abdomen with a phase shift of 180.degree. is optimal, and subsequent trials have suggested that further improvement could be attained with a phase shift of 240.degree..
Another medical procedure which utilizes the cyclical nature of the heart beat and used for improving blood flow is called external enhanced counterpulsation, the goals of which are to decrease the pressure generated by the myocardium during systole and to augment the function of the compromised myocardium by increasing coronary blood flow. External enhanced counterpulsation is performed by compressing the vascular beds within the muscles of the legs and thighs, including the buttocks, in a sequential manner progressing from the calves to the lower and then the upper thighs. This procedure is accomplished by placing and selectively inflating air inflatable bladders around the limbs. Timing of compression is controlled by an electrocardiogram, with the activation of a bladder compression in the vicinity of the electrocardiographic T wave (diastole). This causes increased blood flow and pressure to reach the coronary vessels in diastole at the lowest intramyocardial tension. Compression also increases venous return and cardiac output. The external pressure is then released during the next subsequent R wave (systole), causing systolic unloading and decreasing cardiac work. This treatment improves survival in patients with cardiogenic shock after myocardial infarction, to significantly reduce mortality during acute myocardial infarction, and to improve hemodynamics in chronic angina pectoris. However, the process is complex.
Yet another procedure that takes advantage of the cyclical nature of the heart rhythm is high frequency jet ventilation to augment cardiac stroke volume. Because both systemic venous return and factors determining left ventricular performance may vary over the cardiac cycle, phasic increases in intrathoracic pressure, as produced by high frequency jet ventilation, may differentially affect ventricular preload or afterload if delivered at specific points in the cardiac cycle. When contractility is normal, selective increases of intrathoracic pressure at end-diastole minimally impairs ventricular loading and causes mild hemodynamic deterioration. When cardiac contractility is inpaired and filling pressures elevated, selectively increasing intrathoracic pressure during systole is associated with increased stroke volume despite decreases in left ventricular filling pressure. In acute mitral regurgitation, increasing intrathoracic pressure by increasing the pressure gradient for left ventricular ejection augments cardiac output. This has been demonstrated by utilization of high frequency jet ventilation triggered off either cardiac systolic or diastole in an animal model. As compared with conventional positive pressure mechanical ventilation, systolic synchronous jet ventilation induced a greater increase in stroke volume than diastolic synchronous jet ventilation. However, this procedure is also very complex and is highly invasive to the subject on which it is being performed.
Recently, a large body of evidence has accumulated indicating that increases in the amplitude and frequency of blood flow and intravascular shear stress enhance vascular function and structure. One method for increasing the cycle of blood flow and intravascular sheer stress is exercise. Increases in shear stress on the vascular endothelium caused by increases in blood flow and pulsatility lead to an increase in the release of beneficial mediators such as nitric oxide, prostacyclin, renin, and tissue plasminogen activator. Decreased shear stress causes less of these mediators which promotes development of arteriosclerotic lesions. It is believed that exercise-induced increases in blood flow and shear stress, by increasing the release of nitric oxide and prostacyclin, augment endothelium-dependent vasodilation and inhibit multiple processes involved in atherogenesis and restenosis. Congestive heart failure, which is marked by decreased cardiac output, results in reduced shear stress on the endothelial cells and less beneficial mediator release. As mentioned above, the best way to maintain proper levels is to exercise; however, it is difficult for some people to exercise because of either physical constraints or respiratory problems.
Another problem precipitated by rest is restless legs syndrome and painful legs and moving toes syndrome. Restless legs syndrome is a common problem that is precipitated by rest and relieved by activity. It is treated with a variety of medications, all of which have major side effects.
Finally, according to the National Digestive Diseases Information Clearing House on Constipation, lack of exercise can lead to constipation. Constipation often occurs after an accident or during an illness when one is bedridden and cannot exercise.